What is Boundary-scan?

Boundary-scan (also known as JTAG boundary-scan) is a method of testing modern Printed Circuit Boards (PCBs) after assembly. Using the dedicated test logic built into many of today’s integrated circuits (ICs), boundary-scan checks if each device is correctly inserted and soldered onto the PCB.

To simplify the test infrastructure within a PCB it is common to connect the devices in a serial (daisy chain) formation so that the first device's TDO connects to the next device’s TDI (and so on) to form a so-called scan chain.

To activate the boundary-scan logic, simply pulse TCK while toggling TMS as specified in the TAP state machine map. Once activated, boundary-scan logic controls the device's pins while isolating the primary core functions of the device.